The press secretary accepted that it was “a matter of public record” that – contrary to the PM’s claims – Labour leader Sir Keir Starmer and his party voted for the Christmas Eve deal.
But she claimed that Mr Johnson had been making “a broader point” about Starmer’s earlier support for a second referendum in which he would have voted to Remain.
And she denied that the PM was habitually “sloppy” in his use of language.
As the pair clashed at prime minister’s questions in the Commons, Mr Johnson told MPs: “Last night, our friends in the European Union voted to approve our Brexit deal, which he (Starmer) opposed.”
In fact, Labour voted with the Tories to approve Mr Johnson’s Trade and Cooperation Agreement by 521 votes to 73 on 30 December, with just one Labour rebel joining Liberal Democrats, the SNP and the DUP to vote against.
Asked whether Mr Johnson accepted that – contrary to his claim – Labour did vote for the trade deal, the press secretary said: “Yes, that’s a matter of public record that they did vote in favour of that.”
But she added: “The broader point is that Keir Starmer has consistently backed a second referendum, in which he said he would vote to remain.
“He was making the point that Keir Starmer has consistently opposed Brexit… The point is that we would never have got to this point if is was not for the Conservative party winning the 2019 general election and the prime minister delivering Brexit.”
In fact, Mr Johnson made no reference to Sir Keir’s previous support for a second Brexit referendum.
The press secretary was asked if Mr Johnson would correct the record or apologise for his false claim, but gave no indication that he was planning to do either.
Asked if the PM accepted that he was often sloppy with his language, she replied: “No.”